An automated external defibrillator (AED) is only as reliable as the maintenance behind it. Most modern units run a built-in self-test on a daily, weekly, or monthly cycle, and it is tempting to treat that quiet green light as proof the device is ready. It is not the whole story. A growing body of guidance from manufacturers and safety trainers makes clear that a passing self-test and a genuinely rescue-ready AED are two different things — and the gap between them is where preventable failures happen. Understanding AED maintenance properly, not just trusting the blinking indicator, is what keeps a device functional the one time it is actually needed.
What the Self-Test Actually Checks
The internal self-test built into most AEDs verifies the device’s own circuitry, confirms the battery is delivering adequate charge, and checks that the pad connector is present and recognized. That is a meaningful check, and it is why self-test failures typically trigger a visible status change — a flashing red light or an audible warning tone in place of the steady green confirmation. But the self-test cannot evaluate everything that determines whether a shock will actually reach a patient. It does not know whether the electrode pads have dried out inside a sealed pouch, whether the unit is missing from its wall bracket, or whether someone borrowed the spare razor and gloves from the accessory pouch and never replaced them. Relying solely on the self-test light is a documented gap, not a safe shortcut.
Where Expiration Dates Do the Real Work
Two components carry hard expiration dates that the self-test cannot substitute for: the battery and the electrode pads. AED batteries commonly last between two and five years depending on the manufacturer and model, and many carry a printed expiration or install-by date rather than a simple shelf-life estimate. Electrode pads follow a similar two-to-five-year window, but their failure mode is different and, in some ways, more dangerous: the conductive gel inside a sealed pad packet dries out gradually over time even when the pad is never opened. A dried-out pad can fail to adhere properly to skin, distort the rhythm reading the device relies on to decide whether a shock is advised, or increase electrical resistance in a way that reduces the energy actually delivered — and in some cases raises the risk of skin burns at the contact point. None of that shows up on a self-test screen. It only shows up on the date printed on the packaging, which is why checking it by hand, on a schedule, is not optional.
The Monthly Checklist a Self-Test Cannot Replace
A monthly physical inspection is the standard interval recommended by manufacturers and safety-training organizations alike, and it covers ground the automated test does not reach:
- Status indicator — confirm the visible readiness light is green, not flashing or absent.
- Battery — verify it is installed, seated correctly, and dated well before its expiration.
- Electrode pads — confirm the pouch seal is intact, the printed date has not passed, and the correct adult or pediatric set is present.
- Physical condition — check the housing for cracks or damage and confirm the screen and controls are intact.
- Location and access — confirm the unit is in its designated spot, visible, and not blocked.
- Accessory kit — verify the CPR barrier mask, razor, scissors, and gloves are present and undamaged.
- Documentation — log the inspection date and any issue found, creating a paper trail that a self-test alone cannot generate.
Self-Test Versus Human Inspection
| What it covers | Automated self-test | Monthly human inspection |
|---|---|---|
| Internal circuitry function | Yes | Not directly |
| Battery charge level | Yes | Yes (plus expiration date) |
| Pad gel dryness / expiration | No | Yes |
| Physical damage to housing | No | Yes |
| Correct storage location | No | Yes |
| Accessory kit completeness | No | Yes |
| Written maintenance record | No | Yes |
What Failure Actually Costs
The consequences of an AED that will not perform when called on are not abstract. An expired battery can leave a unit unable to power on at all, or unable to deliver adequate energy for a shock. Expired pads can produce an inaccurate rhythm analysis or fail to deliver the shock the analysis called for. Because survival odds after sudden cardiac arrest fall sharply with every additional minute without defibrillation, a device that fails at the critical moment is not a minor inconvenience — it removes the intervention entirely. There is also an institutional dimension: many workplaces, schools, and public venues that install AEDs operate under state or local rules that expect documented maintenance, and an expired, unmaintained unit that fails during an emergency can raise real liability questions on top of the immediate harm. A programme that stops at "it’s turned on and the light is green" has not actually verified readiness.
Conclusion
The automated self-test built into modern AEDs is a genuine safeguard, but it was never designed to replace a human looking at the device, the dates on its components, and the contents of its accessory kit. Sound AED maintenance treats the self-test as one input among several, not the final word. A short monthly check, paired with disciplined tracking of battery and pad expiration dates, is what actually closes the gap between a device that appears ready and one that will work when a bystander reaches for it.